The 428 CID engine was developed in 1966 to replace the 390 used in the larger cars. The 428 Cobra Jet was essentially a performance version of the 428 FE engine. Launched in April 1968, it was built on a regular production line using a variety of cylinder heads combined with a 735 CFM Holley four-barrel carburetor. The Cobra Jet used heavier connecting rods with a 13/32 rod bolt and a nodular iron crankshaft casting #1UB. A Holman and Moody specially prepared “stripper”, which carried no sound deadener, undercoating, or any optional factory equipment, was used as the introductory press car in 1968. During the mid-1968 model year, a drag racer for the street could be ordered with this optional 428 cu in (7.0 L) Cobra Jet engine which was officially rated at 335 hp all of these Mustangs were issued R codes on their VINs.